Some electronics in integrated circuits are sensitive to temperatures. Temperature-sensitive circuits behave unpredictably under changing temperatures. Ring oscillators are such temperature-sensitive circuits. Ring oscillators can be used as entropy sources to generate true random numbers used in information security, and as components of physical unclonable functions (PUFs), which provide practically unique ID numbers for chips. However, at startup, ring oscillators rapidly change their internal temperatures, which together with circuit noise and environmental effects lead to multiple unpredictable oscillation frequencies. This uncertainty of startup behavior of ring oscillators makes the available entropy unpredictable and the PUF values unreliable, and therefore may harm the information security. Thus, it is desired to stabilize temperature of ring oscillators at startup.
One existing solution to stabilize temperature of temperature-sensitive circuits such as ring oscillators includes placing the temperature-sensitive circuits in thermostat controlled enclosures, which is too large, expensive and slow to be useful. Another existing solution is to modify the temperature-sensitive circuits to improve their thermal properties, which is limited, instable and expensive. A third existing solution is to measure the circuit behavior at manufacturing and compensate for it in the field, which cannot handle the multiple unpredictable oscillation frequencies of ring oscillators.
Therefore it would be desirable to have a system and method that take into account at least some of the issues discussed above, as well as other possible issues.